In recent years, a color liquid crystal display device has rapidly been of very wide prevalence as a flat display of personal computers or the like. Generally, as shown in FIG. 1, a color liquid crystal display device 101 has a structure comprising a color filter 1 and an electrode substrate 2 such as a TFT substrate or the like disposed to face each other providing a gap 3 of about 1 to 10 μm, a liquid crystal compound L filled in the gap 3, and a sealing material 4 which seals the surrounding. The color filter 1 has a structure comprising a black matrix layer 6 formed on a transparent substrate 5 in a predetermined pattern to shield a boundary portion between pixels, a pixel part 7 in which plural colors (generally, the three primary colors comprising red (R), green (G) and blue (B)) are arranged in the predetermined order to form each pixel or recently a pixel part utilizing a hologram, a protective layer 8 and a transparent electrode layer 9 laminated in this order of closest to the transparent substrate. Also, orientation layers 10 are provided in inner surface side of the color filter 1 and an electrode substrate 2 disposed to face each other. Further, pearls 11 having a given particle size are dispersed in the gap 3 as a spacer to keep a cell gap between the color filter 1 and the electrode substrate 2 constant and uniform. A color image can be obtained by controlling a light transmittance of each pixel colored in each color or a liquid crystal layer disposed behind the color filter.
The protective layer 8 formed in the color filter plays a roll of protecting the pixel part and planarizing the color filter when the pixel part is provided to the color filter. The color liquid crystal display device has a problem that if flatness of the transparent electrode layer 9 is damaged due to the presence of ununiformity of gap caused by wave on the surface of the transparent substrate of the color filter, ununiformity of gap between each pixel of R, G and B, or ununiformity of gap within each pixel or the like, mottling or contrast unevenness is caused, and as the result, the quality of image is deteriorated. Thus, the protective layer is required to be flat to a high accuracy.
In the case of dispersing the pearls 11 of particle form as shown in FIG. 1 as spacers, the pearls are dispersed at random regardless of the location behind the black matrix layer 6 or the pixel. If pearls are disposed on a display area, that is, the pixel part, a backlight transmits the pearl portion, the orientation of liquid crystal around pearls is disarranged, and the quality of display image is significantly deteriorated. Therefore, as shown in FIG. 2, instead of dispersing pearls, a columnar spacer 12 having a height corresponding to a cell gap tends to be formed in a superimposing region with a position in inner surface side of the color filter wherein the black matrix layer 6 is formed.
The above-mentioned coloring layer such as the pixel part 7 or the black matrix layer 6, the protective layer 8 and the columnar spacer 12 can be formed with the use of resin. The coloring layer needs to be formed in a predetermined pattern for every pixel of each color or every line of the black matrix. Taking adhesion or sealing property of a sealing portion into consideration, it is preferable that the protective layer 8 can only cover a region on a transparent substrate wherein the pixel part is formed. Further, the columnar spacer 12 is required to be accurately provided in a region in which the black matrix layer is formed, that is, a non-display area. Hence, a method is proposed that a coloring layer, a protective layer and a columnar spacer are formed with the use of a photo-curable resin wherein after selectively exposing a region to be cured, the region can be subject to an alkaline development.
As an alkaline-soluble photo-curable resin, for example, o-cresol novolac epoxy acrylate or the like having a weight average molecular weight of about 2,000 and a carboxyl group defining alkaline solubility is known. However, since the resin uses a monomer component as an acryloyl group defining curability, reliability upon layer-forming is low. That is, for example, there is a risk that a residual monomer unit elutes into a liquid crystal portion or the like. Further, due to a large eluting amount upon alkaline development, layer thickness may be reduced.
As a method to introduce a radical-polymerizable group such as (meth)acryloyl group or the like to provide photo-curability into a molecular structure of a compound, for example, a method is known to prepare a reactant leaving isocyanate group(s) at terminal groups(s) by reacting dials with excess diisocyanate, and react the isocyanate group of the reactant with 2-hydroxylethyl(meth)acrylate or the like to generate urethane(meth)acrylate, thereby, introduce a radical-polymerizable group such as a (meth)acryloyl group or the like to the end. However, by this method, in principle, a (meth)acryloyl group is only introduced to both ends of the molecule. Further, there is a method to perform a radical polymerization with a multifunctional compound having two or more radical-polymerizable groups such as a (meth)acryloyl group or the like contained in one molecule. However, the content of the radical-polymerizable group cannot be controlled. Also, there are problems such as gelation or the like.
Therefore, the inventors of the present invention have proposed a photo-curable resin having a principal chain comprising at least a constituent unit represented by the following Formula 5 and a constituent unit represented by the following Formula 6, and having a (meth)acryloyl oxyalkyl isocyanate compound represented by the following Formula 7 bonded to at least a part of the carboxyl group or hydroxyl group of the principal chain by the reaction of an isocyanate group of the compound (Japanese Patent Application Laid-Open (JP-A) No. 2000-105456):
wherein, R10 is hydrogen atom or a C1-5 alkyl group; R11 is a C2-4 alkylene group; R12 is an alkylene group; R13 is hydrogen atom or methyl atom.
The proposed photo-curable resin has an advantage that it can freely adjust an amount of an alkaline-soluble carboxyl group and an radical-polymerizable (meth)acryloyl group.
However, all of the aforementioned various acrylic curable resins are not sufficient in thermal discoloration resistance. A color filter is exposed to high temperature while assembling a liquid crystal panel, for example, in a process of forming an orientation layer, the color filter is heated at about 250° C. for about 1 hour. In the case of forming a coloring layer or a protective layer of a color filter with the use of an acrylic curable resin, discoloration is caused during the heating process at such a high temperature, and there is a risk to cause problems such as yellowing or deterioration of transparency or the like.
In view of these circumstances, a first object of the present invention is to provide a photocurable resin composition for forming a protective layer, RGB pixels, a black matrix or a spacer of a color filter, which is excellent in thermal discoloration resistance and suitable for forming a minute structure, particularly, a photocurable resin composition having alkaline developing ability.
Also, a second object of the present invention is to provide a color filter of superior performance, which is excellent in thermal discoloration resistance or transparency and excellent in dimensional accuracy of details or evenness.